OP did not specify that it has to be “made today”. I’m curious what your answer would be disregarding era of manufacture.
Well that's a different story, though perhaps not.
While the level of quality of blends from, say, 30 years ago and before, the leaf, blending and processing, are far superior to what's being offered recently, and certainly what's now being offered, that still doesn't mean that I would be completely satisfied with any one of them as my sole smoke. There's a pleasurable thrill from smoking a well preserved blend from decades ago. It's the familiar richness, balance and smoothness of yesteryear. However, very few survivors are well preserved. Buying vintage tins is a craps shoot.
While I smoked a lot of Balkan Sobranie, when it was legitimate, and 759, which I preferred, I wouldn't want either of them as my one smoke.
State Express London Mixture beats the crap out of anything made today, and I wouldn't want it as my one and only. Latakia has a way of wearing out its welcome, even real Latakia, which is by definition, Syrian.
Maybe one of the Rattray's blends, made by Rattray's or by McConnell. Great quality from before everything just became labels.
Maybe Durbar or Royal Yacht, that's Dunhill manufacture. There's little similarity between the actual Dunhill product and the version that STG makes.
Keep in mind that Denmark is where British blends go to die.
Ogden's St Bruno, which is a very different animal from what MacBaren makes (and will soon be made by STG, if they don't discontinue it), has a much richer and more flavorful base than MacBaren's product. St Bruno might be a candidate, the old Ogden's version, but even there I suspect that I would tire of it.
There were a number of blends I smoked years ago, but I don't remember many of them.
The problem for me is that a really great blend requires your attention, really engages your palate, and that wears on me, over time, with every blend I smoke, if I don't switch off between blends. The only antidote might be an OTC blend, since they generally are pleasant, mild, easy to smoke, blends. So maybe Chatham Manor from when it was first released, since it's very like Carter Hall, but without the chemical aftertaste. Or maybe one of the older versions of Sir Walter Raleigh Aromatic, very pleasant and inoffensive.
But probably not.
So I guess my answer is the same.